[pgk]

Please, do not confuse the solvent polarity with the reagents hydrophilicity/lipophilicity. To detail:
1). Polar solvents favor polar reactions, as both these competitive reactions are.
2). The reagents molecules must collide, in order to react. But before their collision, they must contact each other. Thus, similarity in their hydrophilicity/ lipophilicity helps their contact and favors their collision/ reaction (if having moderate kinetic energy), regardless the polarity of the solvent.
3). All the above are not just words because phase transfer catalysis (where, a cationic surfactant or a crown ether are used as catalysts), is based on this principle.

[rolnor]

Did you read my last post, I edited it?

[pgk]

Ethanol is highly hygroscopic and quickly absorbs humidity from the air, up to 4.4 % w/w (azeotrope mixture). Higher absorption of humidity causes evaporation of ethanol, in order to keep constant the azeotrope mass ratio at EtOH/H2O = 95.6/4.4 w/w, which corresponds to a molar ratio EtOH/H2O = 8.5/1.0.
On the other hand, addition of molecular sieves simply delays water absorption and does not really dehydrates ethanol because molecular sieves can absorb water, up to 25% per their mass. Thus and roughly, addition of molecular sieves in ethanol at 4% w/w, can absorb 1% w/w of humidity, only.
In other words, almost all K2CO3 has been hydrolyzed to KOH during the reaction procedure, if using absolute ethanol from a (old and often opened) half-empty bottle (with or without molecular sieves), as a solvent in reactions involving K2CO3 and at dilutions that are in accordance with the ordinary laboratory practice.
PS: Sorry but I was off-line during the weekend.

[wildfyr]

What? Sieves can completely dry ethanol down to 10ppm or so. See that sieve paper I always post.

[pgk]

Yes but it depends from which side you look at the point:
Agreed! Molecular sieves can absorb water, up to 25% w/w. As an example, ethanol containing water 1% w/w can effectively be dehydrated by addition of 4% w/w molecular sieves and ethanol containing water 2% w/w can effectively be dehydrated by addition of 8% w/w molecular sieves and so on.
But if the above ethanol samples are kept in half-empty bottles that are often opened, (humid) air is renewed and the so penetrating, additional amount of moisture cannot be trapped by the contained and already saturated molecular sieves.

[wildfyr]

I think all of us in this discussion including OP understand that if you're going to bother to dry something to the degree that sieves can, you should store it in a shlenk flask and withdraw solvent under a positive pressure dry inert gas flow to replace the volume you are withdrawing. That's the point of a shlenk flask. Isn't this standard procedure?

Typically 10-20% v/v 3A sieves are a good place to start for drying (and keeping dry) hygroscopic solvents.

[pgk]

1). I fully agree.
2). Thinking twice, my phrase “addition of molecular sieves simply delays water absorption and does not really dehydrates ethanol” is wrong and can lead to confusions. Sorry.
The right is: “addition of molecular sieves 3 Å can effectively dehydrate ethanol but precautions are needed during often handling flasks of the so dehydrated ethanol”.

[rolnor]

So, if I need some KOH I can heat K2CO3 to 80°C i absolute ethanol for 40 min.?

[pgk]

As explained above, a bottle labeled “Ethanol Absolute” does not obligatory mean that it really contains absolute ethanol. Consequently, the yield of K2CO3 hydrolysis depends on the water content of the said “absolute ethanol”. At the azeotropic mass ratio (EtOH/H2O = 95.6/4.4 and which is considered to be the maximum water content) up to 33.7 gr K2CO3 per 100 gr of the alcohol, can be hydrolyzed upon heating, giving a mixture of KOH and KHCO3, which is getting more rich in KOH within temperature increase (due to CO2 release), up to the azeotrope point = 78.1oC.
Hint: The use of a condenser is obligatory, otherwise the contained water will azeotropically be evaporated, prior to the complete hydrolysis of K2CO3.

[pgk]

By the way, the water content can satisfactory explain the facile hydrolysis of esters with K2CO3 in methanol(1),(2), which has been posted in this forum in the past (3), with rather unsatisfactory explanations.
1). Total syntheses of (±)-crinine and (±)-buphanisine, Tetrahedron Letters, 28(5), 503-506, (1987)
https://www.sciencedirect.com/science/article/pii/S0040403900957666
2). Isomerization of the Baylis-Hillman adducts using amberlyst-15 as a heterogeneous reusable catalyst: a simple and efficient stereoselective synthesis of (E)-cinnamyl alcohol derivatives, Indian Journal of Chemistry, 45B, 1729-1733, (2006)
http://nopr.niscair.res.in/bitstream/123456789/6587/1/IJCB%2045B%287%29%201729-1733.pdf
3). Hydrolysis of ester with sat. K2CO3 in MeOH, Chemical Forums, (2011)
http://www.chemicalforums.com/index.php?topic=47635.0

[wildfyr]

When I buy pure or absolute ethanol from a reputable company like Sigma or BDH they better damn mean it.

[pgk]

No, they don’t.
A sealed bottle of “Absolute Ethanol” purchased from a reliable supplier (and accompanied with a certificate of analysis), indeed contains absolute ethanol. The real problem is the “often-opened and often-used, half-empty” bottles in the lab, especially when handled by different chemists.
PS: Attention because "pure ethanol" is the azeotropic ethanol, in some European countries.

[rolnor]

So pgk, if you heat a suspension of K2CO3 in dry ETOH in an open flask to 80°C for 40 minutes it will be almost completely converted to KOH? Yes or No?

[pgk]

It depends on much dry your “dry ethanol” is.
So, yes if you add K2CO3 in amounts that respect the stoichiometric ratio of the water content; but you need more than 90 min to ensure the complete thermal decomposition of the simultaneously formed KHCO3 and not in an open flask because the contained water will azeotropically be removed, prior the complete hydrolysis of K2CO3 (you have to reflux in a flask equipped with a cooling condenser).
Note: The temperature will never rise above 78.4oC, which is the boiling point of ethanol and a borderline temperature for the (fast) thermal decomposition of KHCO3.

[rolnor]

Hereinafter I will take your posts with a grain of salt pgk, this simply wrong, K2CO3 will not react in this way at 80°C in ethanol in so short time, even if there is water in stochiometric amount present. Sorry, this is nonsense if you ask me.